1. Field of the Invention
This invention relates to automobile airbags inflators. More specifically, this invention relates to the control of the ignition train of the gas generant used in airbag inflators.
2. Description of Related Art
The safety of automobile passengers has taken important steps forward with the development of automobile airbags. Airbags are inflatable automobile safety devices that help protect a driver or front-seat passenger in a collision. Airbags are most effective when the collision is a head-on or front-angle collision and when they are used in combination with lap and shoulder belts. The typical airbag system consists of a cloth airbag, an inflator, a cover, a can or module to hold the various components, and sensors for detecting the sudden deceleration of the automobile. A computerized control unit typically monitors the system for malfunctions. The sensors, generally mounted on the front of the vehicle and in the passenger compartment, operate on power from the automobile's battery or from the computerized control unit. Typically, airbags are designed to inflate when the automobile strikes an immovable object at more than about ten miles per hour or another automobile at about twice that speed. After an impact, sensors send an electric current to an igniter system or, in some cases to the computerized control unit. This unit evaluates the situation and then sends an electrical impulse to the igniter system. Typically, electrical impulse produces a current which in turn heats a filament, which ignites a pyrotechnic material contained within a capsule. The ignition capsule supplies heat at pressure to ignite gas generating pellets. In most systems, the pellets are made of sodium azide and produce nitrogen gas when they burn. In some systems, pressurized argon gas is used instead. The gas expands quickly and inflates the airbag, which then breaks through a plastic cover in the steering wheel or, on the passenger side, in the dashboard of the automobile. Typically, the whole process takes about 0.1 second from the moment a crash is detected. Once deployed an airbag starts to deflate immediately, venting the harmless gas through openings in the bag or through the bag fabric itself.
A variety of igniter chambers, cavity, and ignition ports have been developed and are widely used in automobile airbags. Traditionally igniter tubes have used cylindrically shaped orifices to control the flow of the ignition material. However, such cylindrically shaped orifices have contributed to relatively poor ignition because of the lack of uniform dispersal of ignition material through the combustion chamber. Because ignition efficiency is directly related to the uniformity of the dispersal of the ignition material or gas generant, through the combustion chamber, improved orifices which provide greater uniformity of gas dispersal, resulting in reduced ignition delay and enhanced performance repeatability of ignition.
For general background material, the reader is directed to U.S. Pat. Nos. 4,272,102, 4,817,828, 4,846,368, 4,928,991, 5,058,921, 5,100,171, 5,222,761, 5,280,946, 5,372,380, 5,458,364, 5,483,896, 5,492,361, 5,505,488, 5,518,268, 5,520,411, 5,533,751, 5,542,702, 5,564,736, 5,623,115, 5,668,345, 5,669,631, 5,681,055, and 5,692,768, each of which is hereby incorporated by reference in its entirety for the material disclosed therein.